The invention relates generally to methods and apparatus for creating an image that is a combination of a main image and an overlay image. In particular, the invention relates to main and overlay images that have had their color resolution reduced. In one embodiment, image is created in a manner that reduces the appearance of artifacts that can result when reduced color resolution images are combined.
In computer systems, overlaying a portion of a main image with one or more smaller images is often desired. The overlay image is frequently text, numbers, or symbols, but may also commonly include icons and graphical images. For example, one may want to overly a photo (a “main” image) with numbers (an “overlay” image) showing the time and date. In a digital image, a main image can be overlaid with an overlay image by replacing pixels of the main image with pixels of the overlay image in the desired region of the main image.
Reducing the color resolution of image data is also often desired in display systems. The human eye is more sensitive to brightness than to color so it is possible to reduce color resolution without much visual impact. Compared to the full-resolution version, a reduced-resolution image requires less memory and memory bandwidth. Reducing color resolution is especially desirable in systems where minimizing memory requirements, power consumption, and cost are important, such as in mobile devices that rely primarily on a battery for power. Examples of such devices include mobile telephones, personal digital assistants, digital cameras, and digital music players.
In display systems, the two techniques may be employed simultaneously: the color resolutions of the main and overlay images are reduced, and the main image is then overlaid with the overlay image. Using the two techniques at the same time, however, can cause artifacts. In particular, one artifact that can result is a gray or off-color fringe that appears around the periphery of the overlay image.
Accordingly, methods and apparatus for creating an image that is a combination of reduced color-resolution main and overlay images in a manner that reduces the appearance of artifacts that can result when the images are combined would be useful and desirable.